This invention relates to an improved shielding holder for radionuclid injection syringes such as the disposable polyethylene syringes currently being used for injecting radioactive substances into a patient's bloodstream for diagnostic or therapeutic purposes. The primary object of the invention is to minimize the radiation exposure to which the technician is subjected in utilizing such a radionuclid syringe while providing for the convenient installation, reliably safe use and easy removability of a syringe from the holder for disposal after use. The invention is herein illustratively described by reference to the presently preferred embodiments thereof; however it will be recognized that certain modifications and changes therein may be made with respect to details without departing from the essential features involved.
The need for more convenient and more safely reliable shielding holders for disposable radionuclid syringes has increased with the expansion of nuclear medicine and the increased emphasis on minimizing radiation exposure of the doctor or technician. With such disposable syringes, typically made of synthetic plastics materials such as polyethylene, radiation shielding by the wall of the syringe body itself is insignificant. Consequently reliance for shielding is placed primarily upon the syringe holder.
It is thus of fundamental importance to design the holder so as to minimize the total dosage of radiation to which the technician is subjected during an injection procedure. Dosage in turn is a function of unabsorbed radiation intensity and exposure time. Exposure time in this case starts with drawing into the syringe a measured amount of radionuclid liquid from a supply container, continues through the process of injecting a measured amount of the radionuclid into the patient's bloodstream and terminates with the steps of releasing of the syringe from the holder, disposal of the used syringe and placement of the holder in a suitable repository for subsequent cleansing. The companion factor determining technician exposure, namely intensity of unabsorbed radiation reaching the technician, is governed by specific absorption of the shielding material and the thickness of that material. Given the type of holder material to be used, however, there are practical limitations on holder wall thickness because of the weight factor and also because of the interference that an unduly thick holder presents in attempting to position the syringe at the necessary shallow angle of incidence to the patient's skin in order to penetrate the vein properly.
In achieving its objectives this invention, while providing a shielding holder of acceptable weight and thickness for suitable handling characteristics, hence one having limited shielding effect, compensates for that limitation by the reduction of technician exposure time it makes possible. As a major contribution in that regard, the improved holder enhances the illumination and visibility of syringe contents and related scale markings so as to facilitate its convenient use with safely reliable accuracy under all working light conditions and without necessity of critical positioning of the holder or of the syringe in the holder for viewing by the technician. In this way the improved holder greatly reduces the chance of quantitative error in the use of the syringe attributable to poor visibility of the radionuclid syringe contents and graduation marks as compared with prior types of holders, especially when used under restricted ambient light conditions or when the user is tired or otherwise not at peak performance.
Prior attempts to provide shielding holders for radionuclid syringes have stressed principally the shielding factor through use of heavy metal holder bodies provided with narrow viewing windows or glass filled slits for observation of the syringe contents and its scale graduation marks. An example is to be found in the disclosure of U.S. Pat. No. 3,596,659. However, such holders, although heavy and cumbersome, are still lacking in shielding capability, and are not easy to use conveniently and with quick efficiency because of viewing difficulties. The steel or lead body of the holder excluding all ambient light except that which can enter through the glass window or slit, makes it often necessary to position the holder with the slit facing as nearly as possible toward the main source of light, and even then the interior of the holder is quite dark and partly masked by reflected light. Moreover if the scale of graduations on the syringe are to be seen clearly through the slit window it is often necessary to rotate the syringe until such graduations make their clearest appearance. These steps and precautions take time and thereby impede the operation, and unless care is taken in this way to secure the clearest attainable view, a mistake can be made either during loading of the syringe or during the injection that follows. Furthermore it is difficult in such cases to mount and seal the glass to the slitted steel or lead sleeve in a manner preventing radiation leakage at the interface. It will be appreciated therefore that the advantage of a dense metal shield in such prior holders can be more than offset by other factors and in the end leave the technician subjected to excessive dosage of radiation and the patient to the possibility of errors due to limited visibility of syringe contents and graduation marks.